diff --git a/Makefile b/Makefile
index c37f784..4ab8962 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@ test: all
 simple-terrain: simple-terrain.c
 	$(CC) $< -o $@
 
-display: display.o roam.o
+display: display.o roam.o square.o
 	$(CC) -lGLEW -lSDL -lGLU $^ -o $@
 
 # Create objects from C source code
diff --git a/roam.h b/roam.h
index 59e552e..5f35641 100644
--- a/roam.h
+++ b/roam.h
@@ -3,25 +3,26 @@
 #include <math.h>
 
 typedef struct Vertex {
-       int x;
-       int y;
-       int z;
-       float xNormal;
-       float yNormal;
-       float zNormal;
-       /* Ajouter des champs ici. */
+	int x;
+	int y;
+	int z;
+	float xNormal;
+	float yNormal;
+	float zNormal;
+	int refCount;
+	/* Ajouter des champs ici. */
 } Vertex;
 
 typedef struct Triangle {
-       Vertex* vApex;
-       Vertex* vLeft;
-       Vertex* vRight;
-       struct Triangle* tLeftChild;
-       struct Triangle* tRightChild;
-       struct Triangle* tBaseNeighbor;
-       struct Triangle* tLeftNeighbor;
-       struct Triangle* tRightNeighbor;
-       struct Triangle* tParent;
+	Vertex* vApex;
+	Vertex* vLeft;
+	Vertex* vRight;
+	struct Triangle* tLeftChild;
+	struct Triangle* tRightChild;
+	struct Triangle* tBaseNeighbor;
+	struct Triangle* tLeftNeighbor;
+	struct Triangle* tRightNeighbor;
+	struct Triangle* tParent;
 } Triangle;
 
 Triangle* initDefaultExample();
diff --git a/square.c b/square.c
new file mode 100644
index 0000000..372e74a
--- /dev/null
+++ b/square.c
@@ -0,0 +1,151 @@
+// get_z()
+#include "roam.h"
+
+#define INIT_VERTEX(v,xx,yy) do { (v)->refCount=0; (v)->x=(xx); (v)->y=(yy); (v)->z=get_z((xx),(yy)); } while(0);
+
+inline Vertex* use_vertex(Vertex* v) { v->refCount++; return v; }
+inline void unuse_vertex(Vertex* v) { if (--(v->refCount) == 0) free(v); }
+
+// ROTATE4(x,r) == x+r % 4
+#define ROTATE4(x,r) ((x+r) & 3)
+
+// L'ordre dans les tableaux est toujours {ne,se,so,no} ou bien {n,e,s,o}.
+typedef enum QTQuadrant { QT_NE = 0, QT_SE = 1, QT_SO = 2, QT_NO = 3 } QTQuadrant;
+typedef enum QTCardinal { QT_N = 0, QT_E = 1, QT_S = 2, QT_O = 3 } QTCardinal;
+
+#define ROT_NE (ROTATE4(QT_NE, r))
+#define ROT_SE (ROTATE4(QT_SE, r))
+#define ROT_SO (ROTATE4(QT_SO, r))
+#define ROT_NO (ROTATE4(QT_NO, r))
+
+#define ROT_N (ROTATE4(QT_N, r))
+#define ROT_E (ROTATE4(QT_E, r))
+#define ROT_S (ROTATE4(QT_S, r))
+#define ROT_O (ROTATE4(QT_O, r))
+
+// QuadTree Node.
+typedef struct QTNode {
+	Vertex* center;
+	Vertex* vertices[4];
+	struct QTNode* children[4];
+	struct QTNode* neighbors[4];
+} QTNode;
+
+void QT_split(QTNode* parent) {
+	// Ne pas split un noeud déjà split.
+	if (parent->children[QT_NE] != NULL) return;
+	
+	int r;
+	QTNode* q[4];
+	for (r = 0; r < 4; r++) {
+		q[ROT_NE] = malloc(sizeof(QTNode));
+	}
+
+	Vertex* new_vertices[4];
+	for (r = 0; r < 4; r++) {
+		// réutiliser le vertex existant (parent->top_neighbor->se_child->so ou bien parent->top_neighbor->so_child->se)
+		if (parent->neighbors[ROT_N] != NULL && parent->neighbors[ROT_N]->children[ROT_SE] != NULL) {
+			new_vertices[ROT_N] = parent->neighbors[ROT_N]->children[ROT_SE]->vertices[ROT_SO];
+		} else {
+			new_vertices[ROT_N] = malloc(sizeof(Vertex));
+			switch (r) { // Pourrait être factorisé, mais on y perdrait en clarté !
+				case 0: INIT_VERTEX(new_vertices[0], parent->center->x, parent->vertices[QT_NE]->y); break;
+				case 1: INIT_VERTEX(new_vertices[1], parent->vertices[QT_SE]->x, parent->center->y); break;
+				case 2: INIT_VERTEX(new_vertices[2], parent->center->x, parent->vertices[QT_SO]->y); break;
+				case 3: INIT_VERTEX(new_vertices[3], parent->vertices[QT_NO]->x, parent->center->y); break;
+			}
+		}
+	}
+	
+	for (r = 0; r < 4; r++) { // Dans le corps de la boucle, positions pour le quadrant ne.
+		q[ROT_NE]->center = malloc(sizeof(Vertex));
+		// Coordonnées du centre de qne = moyenne du center et de parent->vertices[QT_NE].
+		INIT_VERTEX(q[ROT_NE]->center, (parent->center->x + parent->vertices[ROT_NE]->x) / 2, (parent->center->y + parent->vertices[ROT_NE]->y) / 2);
+		use_vertex(q[ROT_NE]->center);
+		
+		q[ROT_NE]->vertices[ROT_NE] = use_vertex(parent->vertices[ROT_NE]);
+		q[ROT_NE]->vertices[ROT_SE] = use_vertex(new_vertices[ROT_E]);
+		q[ROT_NE]->vertices[ROT_SO] = use_vertex(parent->center);
+		q[ROT_NE]->vertices[ROT_NO] = use_vertex(new_vertices[ROT_N]);
+
+		q[ROT_NE]->children[ROT_NE] = NULL;
+		q[ROT_NE]->children[ROT_SE] = NULL;
+		q[ROT_NE]->children[ROT_SO] = NULL;
+		q[ROT_NE]->children[ROT_NO] = NULL;
+
+		// Si le voisin du haut de parent a un se_child, c'est le voisin du haut de qne.
+		if (parent->neighbors[ROT_N] != NULL) {
+			q[ROT_NE]->neighbors[ROT_N] = parent->neighbors[ROT_N]->children[ROT_SE];
+			if (parent->neighbors[ROT_N]->children[ROT_SE] != NULL)
+				parent->neighbors[ROT_N]->children[ROT_SE]->neighbors[ROT_S] = q[ROT_NE];
+		} else {
+			q[ROT_NE]->neighbors[ROT_N] = NULL;
+		}
+		// Si le voisin de droite de parent a un no_child, c'est le voisin de droite de qne.
+		if (parent->neighbors[ROT_E] != NULL) {
+			q[ROT_NE]->neighbors[ROT_E] = parent->neighbors[ROT_E]->children[ROT_NO];
+			if (parent->neighbors[ROT_E]->children[ROT_NO] != NULL)
+				parent->neighbors[ROT_E]->children[ROT_NO]->neighbors[ROT_O] = q[ROT_NE];
+		} else {
+			q[ROT_NE]->neighbors[ROT_E] = NULL;
+		}
+		q[ROT_NE]->neighbors[ROT_S] = q[ROT_SE];
+		q[ROT_NE]->neighbors[ROT_O] = q[ROT_NO];
+		
+		parent->children[ROT_NE] = q[ROT_NE];
+	}
+}
+
+void QT_merge(QTNode* parent) {
+	// Ne pas merge un noeud sans enfants.
+	if (parent->children[QT_NE] == NULL) return;
+	
+	int r;
+	for (r = 0; r < 4; r++) {
+		// Merge récursif des enfants.
+		QT_merge(parent->children[ROT_NE]);
+		
+		// reset à NULL les voisins qui pointaient vers des enfants.
+		if (parent->neighbors[ROT_N] != NULL)
+			if (parent->neighbors[ROT_N]->children[ROT_SE] != NULL)
+				parent->neighbors[ROT_N]->children[ROT_SE]->neighbors[ROT_S] = NULL;
+		if (parent->neighbors[ROT_E] != NULL)
+			if (parent->neighbors[ROT_E]->children[ROT_NO] != NULL)
+				parent->neighbors[ROT_E]->children[ROT_NO]->neighbors[ROT_O] = NULL;
+
+		unuse_vertex(parent->children[ROT_NE]->center);
+		int i;
+		for (i = 0; i < 4; i++)
+			unuse_vertex(parent->children[ROT_NE]->vertices[i]);
+		
+		free(parent->children[ROT_NE]);
+		parent->children[ROT_NE] = NULL;
+	}
+}
+
+QTNode* QT_baseNode() {
+	QTNode* q = malloc(sizeof(QTNode));
+	Vertex** v = malloc(sizeof(Vertex)*5);
+	
+	INIT_VERTEX(v[0], 0, 0);
+	INIT_VERTEX(v[1], +1024, +1024);
+	INIT_VERTEX(v[2], +1024, -1024);
+	INIT_VERTEX(v[3], -1024, -1024);
+	INIT_VERTEX(v[4], -1024, +1024);
+	
+	q->center = use_vertex(v[0]);
+
+	int i;
+	for (i = 0; i < 4; i++) {
+		q->vertices[i] = use_vertex(v[1]);
+		q->children[i] = NULL;
+		q->neighbors[i] = NULL;
+	}
+	
+	return q;
+}
+
+QTNode* QT_example() {
+	QTNode* q = QT_baseNode();
+	return q;
+}